MG132

About: MG132 is a research topic. Over the lifetime, 1499 publications have been published within this topic receiving 56589 citations. The topic is also known as: MG132 & Z-Leu-leu-leu-al.

Effects of proteasome inhibitors MG132, ZL3VS and AdaAhx3L3VS on protein metabolism in septic rats.

Abstract: The ubiquitin–proteasome system (UPS) is a proteolytic system that is localized in cytosol and nucleus and requires ATP and mostly also the cofactor ubiquitin for proteolysis. Proteins to be degraded by UPS are tagged by polyubiquitin chain in a process precisely regulated by a system of ubiquitinating and deubiquitinating enzymes that assure the specificity and control of proteolysis. The proteasome contains protease active sites that account for the cleavage preferences: chymotryptic, tryptic and peptidylglutamyl (Glickman & Ciechanover 2002). The great importance of the UPS is now evident. It is responsible for the breakdown of a large variety of cell proteins, involved in important biological processes, including cell cycle, cell growth, gene expression, DNA repair, stress response and also programmed cell death (Drexler 1998; Hershko et al. 2000). The activated breakdown of myofibrillar proteins, i.e. actin and myosin, in many serious disorders, including cancer, renal failure, acidosis, infections, burns and sepsis, correlates with enhanced activity of the UPS (Tiao et al. 1994; Mitch & Price 2003). Many proteasome inhibitors have been developed (Kisselev & Goldberg 2001). They are divided into several groups according to the chemical structure and proteasome specificity. Most of them (except the fungal metabolite, lactacystine) are based on short oligopeptidic sequences with an electrophilic structure at the C-terminus. This electrophilic structure can be an aldehyde, a boronate (reversible inhibitors), an epoxyketone or a vinylsulfone (irreversible inhibitors) (Lee & Goldberg 1998). Proteasome inhibitors have been introduced as novel therapeutic agents. The first drug of this class is Bortezomib (Velcade®, Millennium Pharmaceuticals, Cambridge, MA, USA), used for the treatment of multiple myeloma. This and other novel proteasome inhibitors are currently undergoing clinical trials as potential treatment for a growing number of other cancer types (Mack et al. 2003; Davis et al. 2004) and other diseases, such as stroke and inflammatory diseases (Di Napoli & Papa 2003). The mechanism of action of proteasome inhibitors predicts large-scale effects in the organism. In general, proteasome inhibitors seem to have manageable adverse effects, e.g. thrombocytopenia, fatigue and peripheral neuropathy (Richardson et al. 2003). As it is presently believed, the proteasome is responsible for a substantial part of proteolysis in physiological state. Several authors studied the ability of proteasome inhibitors to reduce enhanced protein degradation in various catabolic diseases, including denervation, hyperthyroidism, burn and sepsis (Tawa et al. 1997; Fang et al. 1998; Hobler et al. 1998; Fischer et al. 2000), and their findings support the hypothesis that the ubiquitin–proteasome pathway plays a central role in muscle wasting in these catabolic states. The aim of the present study is to evaluate the direct effects of MG132 and new proteasome inhibitors – ZL3VS and AdaAhx3L3VS – on protein and leucine metabolism in skeletal muscle. In addition to evaluating changes in proteolysis, we studied also changes in protein synthesis and leucine oxidation, as the effects of proteasome inhibitors on these parameters are not clear. The experiments were performed by means of isolated muscles of both intact and septic rats. MG132 belongs to the group of peptide aldehydes. It is a strong inhibitor of the proteasome, but inhibits partly also cathepsins and calpains. ZL3VS is a vinylsulphone inhibitor and AdaAhx3L3VS is a vinylsulphone inhibitor with extended peptide portion, which reveals equal potency to all individual catalytic activities of the proteasome (Kessler et al. 2001).

Proteolysis of the barley receptor-like protein kinase RPG1 by a proteasome pathway is correlated with Rpg1-mediated stem rust resistance.

Abstract: In plants, disease resistance mediated by the gene-for-gene mechanism involves the recognition of specific effector molecules produced by the pathogen either directly or indirectly by the resistance-gene products. This recognition triggers a series of signals, thereby serving as a molecular switch in regulating defense mechanisms by the plants. To understand the mechanism of action of the barley stem rust resistance gene Rpg1, we investigated the fate of the RPG1 protein in response to infection with the stem rust fungus, Puccinia graminis f. sp. tritici. The investigations revealed that RPG1 disappears to undetectable limits only in the infected tissues in response to avirulent, but not virulent pathotypes. The RPG1 protein disappearance is rapid and appears to be due to specific protein degradation via the proteasome-mediated pathway as indicated by inhibition with the proteasomal inhibitor MG132, but not by other protease inhibitors.

Distinctive G Protein-Dependent Signaling by Protease-Activated Receptor 2 (PAR2) in Smooth Muscle: Feedback Inhibition of RhoA by cAMP-Independent PKA

Abstract: We examined expression of protease-activated receptors 2 (PAR2) and characterized their signaling pathways in rabbit gastric muscle cells. The PAR2 activating peptide SLIGRL (PAR2-AP) stimulated Gq, G13, Gi1, PI hydrolysis, and Rho kinase activity, and inhibited cAMP formation. Stimulation of PI hydrolysis was partly inhibited in cells expressing PAR2 siRNA, Gaq or Gai minigene and in cells treated with pertussis toxin, and augmented by expression of dominant negative regulator of G protein signaling (RGS4(N88S)). Stimulation of Rho kinase activity was abolished by PAR-2 or Ga13 siRNA, and by Ga13 minigene. PAR2-AP induced a biphasic contraction; initial contraction was selectively blocked by the inhibitor of PI hydrolysis (U73122) or MLC kinase (ML-9), whereas sustained contraction was selectively blocked by the Rho kinase inhibitor (Y27632). PAR2-AP induced phosphorylation of MLC20, MYPT1 but not CPI-17. PAR2-AP also caused a decrease in the association of NF-kB and PKA catalytic subunit: the effect of PAR2-AP was blocked by PAR2 siRNA or phosphorylation-deficient RhoA (RhoA(S188A)). PAR2-AP-induced degradation of IkBa and activation of NF-kB were abolished by the blockade of RhoA activity by Clostridium botulinum C3 exoenzyme suggesting RhoA-dependent activation of NF-kB. PAR2-AP-stimulated Rho kinase activity was significantly augmented by the inhibitors of PKA (myristoylated PKI), IKK2 (IKKIV) or NF-kB (MG132), and in cells expressing dominant negative mutants of IKK (IKK(K44A), IkBa (IkBa (S32A/S36A)) or RhoA(S188A), suggesting feedback inhibition of Rho kinase activity via PKA derived from NF-kB pathway. PAR2-AP induced phosphorylation of RhoA and the phosphorylation was attenuated in cells expressing phosphorylation-deficient RhoA(S188A). Our results identified signaling pathways activated by PAR2 to mediate smooth muscle contraction and a novel pathway for feedback inhibition of PAR2-stimulated RhoA. The pathway involves activation of the NF-kB to release catalytic subunit of PKA from its binding to IkBa and phosphorylation of RhoA at Ser(188).